Transmitter tube circuit



P 1939- w. BUSCHBECK 2,153,112

TRANSMITTER TUBE C IRGUIT Fi led May 27, 1956 WERNER BUSCHBECK IBYV ATTORNEY Patented Apr. 4, 1939 PATENT OFFICE.

TRANSMITTER TUBE omourr Werner Buschbeck, Berlin, Germany, assignor to Teiefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Appiic'ation May 27,1936, Serial No. 82,042

I In Germany June 18, 1935 j 4 Claims. (01. 179-171) At the transition from the operating state of sub-normal or normalvoltage of a tube having threeor four electrodes to the state of excess voltage, it is known thatthe grid or screen grid current greatly increases whereby the tubemay be endangered owing to excessive heating of the respective grids. To overcome this drawbackto a certain degree, it is known forquite some time that instead of applying a constant biasing potential to the grid or screen grid, the grid-potential is to be made dependent upon the respective grid current by means of ohmic resistors placed in series to the constant biasing potential, In this case, the .grid current can increase but slightly since it produces a negative grid potential at the ohmic resistor.

This measure can be successfully applied in all tubes with reliable grid currents. But it becomes dangerous in all cases in which the appearance of a secondary emission might be expected, thus especially in all tubes having filaments requiring only a low heating. If, for example, in the course of time the grids become activated, a single detuning or excessive load no matter how short it may be, or any other phenomenon leading from the normal, usually somewhat excessive voltage state to the sub-normal operating state, is sufiicient to cause in the tube the condition of the reversed grid current. This means that in the moments of highest positive grid potential, the secondary electrons produced at the grid will be attracted by the anode so that the number of electrons leaving the grid is greater than that of the arriving electrons, and therefore the grid current flows in the wrong direction. In this moment also the voltage drop at the grid leak resistor will be reversed, due to potential drop produced in the grid resistor, the grid becomes more positive, and the secondary emission increases etc., until the tube breaks down (increase of grid and anode current) causing in the majority of cases a damage to the tube or to transmitter parts, and at any event a failure of the transmitter.

This dangerous condition can be avoided in accordance with the invention by the insertion into the outer lead-ins to one or several grids, resistors depending upon direction, such that a reversed grid current cannot produce a positive grid potential. In describing the invention reference will be made to the single figure which shows a tube circuit including the tube protecting means of the present invention.

As resistor depending upon direction, a dry detector or any other detector may serve, in-

serted in the grid circuit in such a manner that it offers a high resistance to the grid current of normal direction, and consequently a negative voltage drop will be produced "through said resistor. However, on reversal of the grid current only the constant biasing potential appears at the grid, because the detector acts as short circuit and therefore no positive grid potential can be produced therethrough.

resistance in the direction of blocking.

The direction of the normal grid current is indicated in the figure by arrows. The normal grid current sets up negative bias acting through the resistor on the grid, whereas when the grid current is reversed no positive potential which could oppose the constant biasing potential can be produced at the resistor W since the detector G acts as short circuit for said current.

Obviously the invention may also be applied to other grids such as screen grids for instance as shown in the single figure. In this case, the detector G, at a. reversal of the screen grid current, prevents the voltage, which is as such positive, from attaining too high a value. Here again the detector or rectifier may be shunted by a resistance W1.

I claim:

1. In a signalling system, a tube relay having a cathode, an anode, and a grid electrode, alternating current circuit means for impressing wave energy on said cathode and said grid electrode, a source of direct current and a substantially unilateral device connected in series between said. grid electrode and said cathode, alternating current circuit means for deriving wave energy from said cathode and said anode, said substantially unilateral device being of high impedance to current flow in one direction and of low impedance to current fiow in the other direction and being poled to permit said source of potential to apply the desired operating potential to said grid electrode and normal current to fiow between said grid electrode and cathode and to present a short circuit to a fiow of current in the wrong direction between said grid electrode and cathode caused by secondary emission from said grid to thereby prevent the application of abnormal potentials to said grid electrode.

2. In a signalling system, a tube relay having a cathode, an anode, and a plurality of grid-like electrodes, direct current energizing means for each of said grid electrodes including a source of direct current and a unilateral device in series between each of said grid electrodes and said cathode, a high resistance in shunt to each unilateral device, circuit means for impressing wave energy on said cathode and one of said grid-like electrodes connected in series between said grid and its direct current energizing means, circuit means for deriving wave energy from said cathode and said anode, said unilateral devices being poled to permit said sources of potential to apply the desired operating potentials to said grid electrodes and to permit normal currents to flow between said grid electrodes and said cathode and to substantially prevent reversal of flow of current between said grid electrodes and cathode from applying other potentials to said grid electrodes.

3. An electron discharge device having a cathode and at least one additional electrode, circuit means for applying controlling potentials between said cathode and said additional electrode,

circuit means for permitting a normal flow of current between said cathode and said additional electrode, resistive means in said last circuit for producing a potential drop proportional to the 7 current flow therein to polarize said additional electrode relative to said cathode, and means for substantially preventing a reversal of flow of current between said cathode and said additional electrode from abnormally polarizing said additional electrode relative to said cathode comprising a rectifier connected in shunt to said resistive means and poled to prevent production of a potential drop in said resistive means due to flow of current in said circuit means except in the normal direction.

4. In a signalling system, a tube relay having a cathode and a grid-like electrode, circuits for impressing potentials to be amplified or relayed on electrodes of said tube and for deriving amplified or relayed potentials from the anode and cathode of said tube, direct current energizing means for said grid electrode including a source of direct current and a substantially unilateral device in series between said grid electrode and said cathode, said unilateral device being poled to be of high impedance to normal flow of current from said cathode to said grid electrode to permit the desired operating potential to be applied to said grid electrode and being of low impedance to an abnormal flow of current from said grid electrode to said cathode to prevent the application of abnormal potentials between said grid electrode and cathode and a high resistance in shunt tosaid unilateral device to facilitate the application of normal potentials to said grid electrode and the flow of normal current between said grid electrode and said cathode.

WERNER BUSCHBECK. 

